With reference to FIG. 1, a schematic diagram of a simplified example of a vehicle having a surge tank for de-aerating coolant is illustrated. In FIG. 1, the vehicle 10 comprises an engine 12 and a radiator 14 through which coolant is circulated, at least at selected times, to cool the coolant for use in removing heat from the engine. Other components may also be cooled by the coolant such as a transmission 16 and an exhaust gas recirculation cooler (e.g., EGR cooler) not shown in this figure. The coolant may also be used to provide energy to or remove energy from an HVAC (heating ventilation and air conditioning) system of the vehicle. One specific example of a vehicle is a truck, such as a heavy duty or medium duty truck used in long hauling operations or a truck tractor used for such purposes. Land vehicles are particularly desirable applications in which such surge tanks would be used. In FIG. 1, segments of the coolant recirculation conduits are indicated by the numbers 18, 20 and 22. In the example of FIG. 1, aerated coolant from the engine passes via a conduit 24 to an inlet to a surge tank 26. In addition, aerated coolant passes through a conduit 28 from radiator 14 to an inlet to the surge tank 26, which may separate from or in common with the inlet that receives aerated fluid from conduit 24. Air is removed from the coolant as it passes through the surge tank 26. The de-aerated coolant is returned to the engine via a conduit 30 in FIG. 1.
There are a number of reasons for de-aerating coolant. For example, poor de-aeration of coolant can result in cavitation of an engine water pump, pitting of engine liners, engine overheating, cab HVAC system failures, EGR cooler erosion, and other drawbacks. Modern truck engines have relatively high fluid flow rates to a surge tank, such as in excess of four gallons per minute. As a result, it becomes more difficult to de-aerate the coolant. In addition, high fluid flow rates into a surge tank can result in fracturing air bubbles into microbubbles (e.g., pin sized bubbles) which are even more difficult to remove from the coolant.
It is known to make surge tanks out of plastic for weight and cost saving purposes. However, because of the high temperatures often reached by coolant, plastic can tend to soften when used. As a result, plastic surge tanks are typically provided with reinforcing baffles. However, high coolant flow rates into surge tanks with baffles increases the foaming (formation of small bubbles) when the entering liquid impacts the baffles. Also, because extremely small bubbles entrained in fluid are difficult to separate, bubbles formed from fracturing larger bubbles are more easily carried through a surge tank, resulting in poorer de-aeration of the coolant. To reduce the possibility of small foam formed bubbles entering the fluid and being carried through a surge tank, some engine manufacturers have issued specifications directing that fluid inlets to surge tanks be positioned above the level of fluid in the surge tank so that foam can escape into an air gap above the fluid level.
Other advantages of plastic surge tanks comprise the ability to make the surge tanks transparent or translucent for better visual inspection of fluid levels within the surge tanks, lower cost per piece and the fact that plastic can be molded readily into odd shapes.
A need exists for improved surge tank designs and related methods.